Agaricus xanthodermus (Yellow Stainer): Identification of this Toxic Fungi

Agaricus xanthodermus
The yellow stainer, Agaricus xanthodermus Genev. Credit: ‘Chilepine’
Credit: © Br. Alfred Brousseau, Saint Mary’s College.


Kingdom Fungi
Phylum Basidiomycota
Class Basidiomycetes
Order Agaricales
Family Agaricaceae
Genus Agaricus


Agaricus meleagris var. grisea (A. Pearson) Wasser
Ukr. bot. Zh. 35(5): 516 (1978)

Agaricus pseudocretaceus Bon
Docums Mycol. 15(no. 60): 34 (1985)
Agaricus xanthodermus var. griseus (A. Pearson) Bon & Cappelli
Docums Mycol. 13(no. 52): 16 (1983)
Agaricus xanthodermus var. lepiotoides Maire
Agaricus xanthodermus Genev.
Bull. Soc. bot. Fr. 23: 28 (1876) var. xanthodermus
Pratella xanthoderma (Genev.) Gillet
Champignons de France. Tableaux Analytiques des Hyménomycétes (Alençon): 129 (1884)
Psalliota flavescens Richon & Roze
Psalliota xanthoderma (Genev.) Richon & Roze
53 (1885)
Psalliota xanthoderma var. grisea A. Pearson
Trans. Br. mycol. Soc. 29(4): 204 (1946)
Psalliota xanthoderma var. lepiotoides (Maire) Rea
Brit. basidiomyc. (Cambridge): 85 (1922)

Common names

Yellow stainer
Agaric jaunissant, Psalliote jaunissante (French)
Prataiolo – Falso prataiolo (Italian)
Karbolchampignon (German)
Pieczarka karbolowa (Polish)

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Cap: usually 6-10 cm diameter (up to 15 cm). It is initially convex, with some young specimens having a squarish shape, though flattening with age. It is whitish, with light brown tints towards the center. The cap is dry and smooth, but can be scaly when old. The gills of this mushroom progress from pale-pink to a chocolate color.
Spore print: brown.
Stem: bulbous with a skirt-like ring. Microscopically, there are club-shaped cheilocystidia.
Spores: 6-7 × 3-4 µm.

Agaricus xanthodermus looks similar to the field mushroom (Agaricus campestris), but when the surface of the cap or stem is scraped it stains a distinct yellow colour. With time, the yellow stain fades to dull brown. Also, it has an ‘inky’ (phenolic) smell that is stronger at the base of the stem. Upon cooking the odor becomes more pronounced. Treatment of this mushroom with potassium hydroxide (KOH) turns the flesh orange-yellow.


Agaricus xanthodermus is one of the most commonly ingested poisonous mushrooms (Hender et al., 2000). If eaten, symptoms may include abdominal cramps, nausea, vomiting and diarrhea. Less common symptoms include headache, dizziness, sweating and drowsiness. It should be noted that some people haven eaten this species without apparent ill effects.

Also, A. xanthodermus contains a molecule, 4,4′-dihydroxy-azobenzene, that in high doses, is carcinogenic to mice. At lower concentrations, however, the azo compound does not have tumor-inducing effects (Toth et al., 1989).

Although other edible Agaricus species, such as A. augustusA. arvensisand A. silvicola, turn yellow to a greater or lesser extent, they do not display such an intense reaction as A. xanthodermus. This species is commonly found in grass under trees or in parks, but seldom in deep forest (Kerrigan et al., 2005). It is found in North America, Europe, and Africa.

Bioactive compounds

A number of chemicals have been extracted from Agaricus xanthodermus, including:

  • 4,4′-dihydroxy-azobenzene
  • p-quinol
  • 4,4′-dihydroxybiphenyl
  • phenol

The concentration of phenol in the fruitbodies was found to be high enough to account for the toxicity of the mushrooms (Gill and Stauch, 1984).

Elemental composition

The levels of calcium, magnesium, iron, manganese, lead, chromium and cadmium in Agaricus xanthodermus was determined in a South African study. Agaricus xanthodermus had Ca (204), Mg (660), Fe (306), Mn (30), Cr (16.2), Pb (50.6) and Cd (29.5) mg/kg by dry weight (Jonnalagadda et al., 2006). The relatively high cadmium concentration corroborates a previous study that reported high cadmium in this species (Yesil et al., 2004)

Psalliotin, the antibiotic found in A. xanthoderma, is light sensitive (Atkinson, 1954). It was later shown that work-up of the methanolic extract in the presence of sodium sulfite yielded the compound agaricin, which has strong antibiotic and cancerostatic properties (K. Dornberger, W. Gutsche, R. Horschak, A. Zureck, Z. Ally. Mikrubiol. 18 (1978) 647; K. Dornberger, H. Lich, C. Schonfeld, H. Knoll, DDRPat. 132878 (15. Nov. 1978); Chem. Abstr. 91 (1979) P 87622e.). The structures of compounds responsible for the antibiotic activity and the yellow discoloration of the fungus were later determined (Hilbig et al., 1985):

“When 3 is dissolved in water and treated with sodium hydrogen carbonate the solution immediately turns yellow in color on being exposed to air. Oxidation proceeds especially smoothly upon addition of sodium periodate: 1 can be recovered by extraction with ethyl acetate; it is identical in all respects with the yellow pigment from A. xanthoderma. It can therefore be assumed that the toadstool contains leucoagaricone 3 which is oxidized to 1 by atmospheric oxygen (oxidases) when the fruiting body is damaged.”


The following sites all have something interesting or useful to say or show about the yellow stainer:

California fungi
Mushroom Expert
Bioimages (several pictures)


Atkinson N. Antibacterial activity in members of the higher fungi .1. Cortinarius rotundisporus and Psalliota xanthoderma Genev. Aust J Exp Biol Med Sci. 1946 24(3):169-73.

Atkinson N. Psalliotin, the antibiotic of Psalliota xanthoderma. Nature. 1954 174(4430):598.

Atkinson N. Antibacterial activity in members of the higher fungi. II. Psalliotin, the antibiotic of Psalliota xanthoderma. Aust J Exp Biol Med Sci. 1955 33(2):237-42.

Callac P, Guinberteau, J. Morphological and molecular characterization of two novel species of Agaricus section Xanthodermatei. Mycologia. 2005 97(2):416-24.

Dornberger K, Ihn W, Schade W, Tresselt D, Zureck A, Radics L. Antibiotics from Basidiomycetes – evidence for the occurrence of the 4-hydroxybenzenediazonium ion in the extracts of Agaricus xanthodermusGenevier (Agaricales). Tetra Lett. 1986 27(5):559-60.

Dornberger K, Ihn W, Schade W, Tresselt D, Zureck A, Radics L. Antibiotics from basidiomycetes – 4-hydroxybenzenediazonium ion, an antibiotically active metabolite of the basidiomycete Agaricus xanthodermus-Genevier. Pharmazie. 1987 42(3):212-.

Gill M, Strauch RJ. Constituents of Agaricus xanthodermus Genevier: the first naturally endogenous azo compound and toxic phenolic metabolites. Z Naturforsch [C]. 1984 39(11-12):1027-9.

Hender E, May T, Beulke S. Poisoning due to eating fungi in Victoria. Aust Fam Physician. 2000 29(10):1000-4.

Hilbig S, Andries T, Steglich W, Anke T. Antibiotics from Basidiomycetes .22. the chemistry and antibiotic-activity of the toadstool Agaricus xanthoderma (Agaricales). Angewandte Chemie. 1985 24(12):1063-5.

Hocking CS. The purification of antibiotic extracts of Psalliota xanthoderma. Aust J Exp Biol Med Sci. 1950 28(5):585-88.

Jonnalagadda SB, Pienaar DH, Haripersad K. Elemental distribution in selected Agaricus and Rhizina mushrooms in South Africa. J Environ Sci Health A Tox Hazard Subst Environ Eng. 2006 41(3):507-14.

Kerrigan RW, Callac P, Guinberteau J, Challen MP, Parra LA. Agaricus section Xanthodermatei: a phylogenetic reconstruction with commentary on taxa. Mycologia. 2005 97(6):1292-315.

Mitchell AD, Walter M. Species of Agaricus occurring in New Zealand. New Zeal J Bot. 1999 37(4):715-25.

Pope KG. The toxicity of potassium chloride and of extracts of Psalliota xanthoderma for mice and rabbits. Aust J Exp Biol Med Sci. 1950 28(3):361-6.

Toth B, Patil K, Taylor J, Stessman C, Gannett P. Cancer induction in mice by 4-hydroxybenzenediazonium sulfate of the Agaricus xanthodermus mushroom. In Vivo. 1989 3(5):301-5.

Wood, WF, Watson, RL, Largent, DL. Phenol, the odour compound from Agaricus praeclaresquamosus. Biochem System Ecol. 1998 26(7):793-4.

Yesil OF, Yildiz A, Yavuz O. Level of heavy metals in some edible and poisonous macrofungi from Batman of South East Anatolia, Turkey. J Environ Biol. 2004 25(3):263-8.

2 thoughts on “Agaricus xanthodermus (Yellow Stainer): Identification of this Toxic Fungi”

  1. I expect you are very busy in the forest right now but perhaps you can help.
    In Pyreneean foothills last week: mushroom ‘identical’ to Ag. Xanthodermus found in a row in grass at tree roots. Did NOT stain yellow anywhere, had a blocky head when young, very thick soft veil, skimpy ring, smooth stem tapered at cap junction. Didn’t do microscopy. Chopped and cooked them, turned very slightly straw-coloured. Meal went down as normal no problems. Next day leftovers in a very small amount produced nausea and vomiting. I’m sure they are still growing. Any ideas? all the best Maggie

    • This is why I hate online mushroom identification 🙂
      It’s really, hard to say without physically seeing the mushroom but to me it sounds like you ate Agaricus xanthodermus. There is a reason it is the most commonly eaten poisonous mushrooms!


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